I'm going through the process up upgrading my computers to Windows 10. The primary desktop is done and functional, now I'm into the spare computers. Spare desktop #1 took the upgrade just fine. I don't care for the new look of Firefox, so on the primary desktop I had switched to Waterfox some time ago, and I run it with the Classic Theme Restorer add-on. So I installed Waterfox on the spare, went to add-ons to install Classic Theme Restorer, and ... no joy! Since it doesn't work with Firefox v. 57 and newer, Mozilla has taken it down from their add-on site. So I now cannot get either Firefox or waterfox to look like the browser on my primary computer.
NOT a happy camper.